Minwah,
Now that I've submitted a couple games to the controls.dat project (more coming

) I can truly see the power of this thing.
It would be really great if a developer (yourself for example) were to code a "control panel layout designer" that would allow the user to place controls representing their actual controls (color, and everything) on a canvas and tie them to MAME controls. The designer could come with a canned set of controls, maybe as jpg's or something. The user could add their own custom ones, too. That way it would truly represent what was there.
Then, when someone walks up and starts a game, MAMEWAH brings up a cue card highlighting which buttons on that specific control panel are which actual controls from the arcade.
I think that would be the best thing since sliced bread

Seriously, almost every single person that walks up to my arcade machine starts a game and says something like "ok, which button is jump"
Oh yeah, I'll plug the controls.dat project, too. Everyone - GO CONTRIBUTE. It's pretty easy to do. If you feel intimidated (I did), do an easy one that doesn't have many controls to start with (like donkey kong jr. or donkey kong 3

) Then you'll see how easy it really is to do.